During the production of fibers for papermaking, wood or other fiber source is ground into chips or mechanically treated such that the chips may be broken down further and refined into individual fibers.
Disk refiners are used with either high consistency stock containing eighteen to sixty percent fiber by weight or with low consistency pulp of two to five percent fiber dry weight. In high consistency applications the disk refiner acts to break down clumps of fibers into individual fibers. In low consistency applications the disk action is used to increase the freeness or bonding capability of the individual fibers. A refiner disk consists of a disk-shaped steel or steel-alloy casting which has a multiplicity of generally radially extending bars integrally cast with the surface of the disk. A first refiner disk is mounted on a rotor for rotation and another disk is held opposed to the first refiner disk, either by rigid mounting or by mounting on an opposite rotating rotor. The refiner disks, as they move past each other, separate and refine the wood pulp as it passes between the opposed disks.
Typically, each disk is comprised of a number of radially outwardly positioned rings which are independently bolted to the rotor and to the non-rotating surface. A disk refiner is typically only one station in a capital-intensive processing stream. To maximize productivity of the papermaking system, downtime of the refiner must be minimized. Bolting the disk sectors through the refining bar faces to the support surfaces provides ready access to the fasteners with minimal disassembly of the refiner. Due to the extensive wear on the refining bars, the rings must be removed at regular intervals and repaired or replaced. Because of the different configurations and positions of the refiner bars on inner and outer rings, the rings do not wear at equal rates. For maximum usage, one set of inner rings may remain in place while several sets of outer rings are removed. With the long-term exposure of the inner rings to wear, the heads of the bolts which hold the inner rings in place are eroded, making the eventual removal of the inner rings difficult.
What is needed is a refiner disk construction which prevents the erosion of inner disk ring bolt heads.